In lay betting you are effectively saying: "I believe this horse will lose - anyone who thinks it will win can bet against me."
Usually you are risking a large sum of money for a relatively small return.
As a result it is betting for the brave - or, as Panorama reveals, those with information the rest of us do not have.
The fear is that professional gamblers will try to acquire privileged information - from owners, jockeys or trainers - on a horse's likely performance to give themselves an unfair advantage on these sorts of bets.
Tipping does of course happen and the British Horseracing Authority (BHA), the official governing body of British horseracing, says that this is fine, so long as it happens in the public domain - allowing all gamblers equal opportunity to benefit from the information.
But the BHA has told jockeys that if they regularly give information, which is not in the public domain, to contacts who then use it to lay bet on horses to lose, they risk being disciplined.
That, they say, is the difference between tipping and what in the City would be called "insider dealing".
And the BHA says it will not need proof of financial gain to move against a jockey - that a pattern of contact with gamblers, even through a go-between, will be sufficient.
Through months of investigation Panorama has discovered just why the racing authorities have become so concerned that ordinary punters were not betting on a level playing field.
Racing's Dirty Secrets shows how it is possible to make hundreds of thousands of pounds from betting on horses to lose, and reveals why it is so tempting to stack the odds unfairly by gaining insider knowledge and influence.
Panorama: Racing's Dirty Secrets will be on BBC One at 9:30pm on 30 July